Many industrial applications require heat exchangers to condense or cool vapor containing non-condensable gases. Examples of such applications are condensers for power plants, particularly power plants using organic working fluids, coolers in oil refineries, etc. In each case, the venting of the non-condensable gases is important in order to prevent build-up of these gases on heat exchanger surfaces, a situation that adversely affects the transfer of heat through the affected surfaces.
Where the heat exchanger is air-cooled, and is of the type having a plurality of heat exchanger tubes organized into a plurality of vertically spaced banks of tubes connected to an inlet header that receives the vapor and non-condensable gases (hereinafter referred to as a heat exchanger of the type described), the temperature of the air that cools the tubes increases as the air passes around the tubes and through successive banks. Generally, the air flows vertically upwardly so that the coolest air is in contact with the lowermost bank of tubes, and the warmest air is in contact with the uppermost bank. Thus, the temperature and pressure inside each bank of tubes will be different; and disturbances in the flow of vapor and liquid condensate have been found to occur, particularly when the vapor being condensed is heavier than the non-condensable gases contained in the vapor. Such disturbances adversely affect the operational characteristics of the condensers and often erratically affect the efficiency of the heat exchanger.
In condensers for Rankine cycle power plants utilizing organic working fluids, it is conventional to provide a heat exchanger of the type described wherein one or more banks of tubes are inclined relative to the horizontal, one end of each of the tubes being connected to an inlet header, and the other end of each of the tubes being connected to a collection header located at an elevation above the inlet header. In this manner, the vapor in each bank flows upwardly in the tubes thereof in contact with the upper, interior portion of each tube, and the condensate, produced by the exchange of heat between the vapor and the air outside the tube, flows, downwardly in contact with the lower, interior portion of each tube. Non-condensable gases in the vapor admitted into the condenser, being lighter than the vaporized organic working fluid at the same temperature and pressure, collect at the top of the collection header which is located at the highest point in the system. These non-condensables can be vented from the collection header; but the differences in pressure in each bank appear to interfere with the flow of the non-condensables with the result that not all of the non-condensables are vented and some are drawn back into the system or adversely affect the heat transfer characteristics of the condenser.
An object of the present invention is to provide a new and improved heat exchanger which overcomes the above-described deficiencies of prior art heat exchangers of the type described.